Single-focus optical system and optical apparatus using the same

ABSTRACT

A single-focus optical system includes in order from an enlargement side, a first lens unit, and a second lens unit having a positive refractive power. A lens component is one of a single lens and a cemented lens. The first lens unit includes a reduction-side negative lens component closest to the reduction side, and in addition, the first lens unit includes not less than three negative lens components including the reduction-side negative lens component. The second lens unit includes in order from the enlargement side, a first positive lens, a second positive lens, a first negative lens, and a third positive lens, and all airspaces in the second lens unit are constant at a time of focusing.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of InternationalApplication No. PCT/JP2015/065798 filed on Jun. 1, 2015, the entirecontents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a single-focus optical system and anoptical apparatus using the same.

Description of the Related Art

As a type of an image forming optical system having a high imagingperformance, a Gaussian type has been known. A Gaussian type opticalsystem includes in order from an object side, an object-side unit havinga positive refractive power and an image-side unit having a positiverefractive power.

The object-side unit includes two to three positive lenses and onenegative lens. This negative lens is cemented to the positive lensimmediately before the negative lens in some cases. Moreover, theimage-side unit includes one negative lens and two to three positivelenses. This negative lens also, is cemented to the positive lensimmediately before the negative lens in some cases.

Moreover, in the Gaussian type optical system, a shape on the objectside and a shape on an image side is, by and large, symmetrical about acentral portion thereof, and moreover, the Gaussian type optical systemhas a concentric shape. In the concentric shape, a center of curvatureof two lens surfaces in each lens is positioned near the centralportion.

Accordingly, in the Gaussian type optical system, even with a largeaperture ratio, each aberration is corrected favorably to some extent.However, when an attempt is made to realize an imaging performancesuperior to that of the conventional one, in the Gaussian type opticalsystem, an angle of view slightly smaller than 50 degrees is the limit.When an attempt is made to realize the angle of view not smaller than 50degrees in the Gaussian type optical system, in particular, correctionof a spherical aberration and a coma becomes difficult. Moreover, in anoptical system based on the Gaussian type, the optical system issusceptible to be large-sized.

On the other hand, from a viewpoint that an F-number is small, apartfrom the Gaussian type, Sonnar type and Ernostar type have been known astypes of image forming optical system. Since a back focus is susceptibleto become short in these types, adopting an optical system of thesetypes is advantageous from a point of shortening an overall length ofthe optical system. However, these types have a drawback that it is notpossible to widen the angle of view easily.

Various types of wide-angle taking lenses in which these issues aresolved, have been proposed. In the wide-angle taking lens that has beenproposed, an F-number is about 1.4. As examples of an optical system ofwide-angle taking lens with a wide angle of view and a small F-number,optical systems disclosed in Japanese Patent Application Laid-openPublication No. 2012-226309, Japanese Patent Application Laid-openPublication No. 2004-101880, Japanese Patent Application Laid-openPublication No. 2009-109723, Japanese Patent Application Laid-openPublication No. 2010-039340, Japanese Patent Application Laid-openPublication No. 2010-097207, and Japanese Patent Application Laid-openPublication No. 2011-059290 are known.

SUMMARY OF THE INVENTION

A single-focus optical system according to the present invention whichforms a conjugate relationship between a conjugate point on anenlargement side at a long distance and a conjugate point on a reductionside at a short distance, comprises in order from the enlargement side,

a first lens unit, and

a second lens unit having a positive refractive power, wherein

a lens component is one of a single lens and a cemented lens, and

the first lens unit includes a reduction-side negative lens componentclosest to the reduction side, and

in addition, the first lens unit includes not less than three negativelens components including the reduction-side negative lens component,and

the second lens unit includes in order from the enlargement side, afirst positive lens, a second positive lens, a first negative lens, anda third positive lens, and

all air spaces in the second lens unit are constant at a time offocusing.

Moreover, an optical apparatus of the present invention comprises

an optical system, and

an image pickup element which is disposed on a reduction side, wherein

the image pickup element has an image pickup surface, and converts animage formed on the image pickup surface by the optical system to anelectric signal, and

the optical system is the abovementioned single-focus optical system.

Moreover, another optical apparatus of the present invention comprises

an optical system, and

a display element which is disposed on a reduction side, wherein

the display element has a display surface, and

an image displayed on the display surface is projected on theenlargement side by the optical system, and

the optical system is the abovementioned single-focus optical system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A, and FIG. 1B, FIG. 1C, FIG. 1D, and FIG. 1E are across-sectional view and aberration diagrams respectively, of asingle-focus optical system according to an example 1;

FIG. 2A, and FIG. 2B, FIG. 2C, FIG. 2D, and FIG. 2E are across-sectional view and aberration diagrams respectively, of asingle-focus optical system according to an example 2;

FIG. 3A, and FIG. 3B, FIG. 3C, FIG. 3D, and FIG. 3E are across-sectional view and aberration diagrams respectively, of asingle-focus optical system according to an example 3;

FIG. 4A, and FIG. 4B, FIG. 4C, FIG. 4D, and FIG. 4E are across-sectional view and aberration diagrams respectively, of asingle-focus optical system according to an example 4;

FIG. 5 is a cross-sectional view of an image pickup apparatus;

FIG. 6 is a front perspective view showing an appearance of the imagepickup apparatus;

FIG. 7 is a rear perspective view of the image pickup apparatus;

FIG. 8 is a structural block diagram of an internal circuit of maincomponents of the image pickup apparatus; and

FIG. 9 is a cross-sectional view of a projection apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments and examples of a single-focus optical system and an opticalapparatus using the same will be described below in detail by referringto the accompanying diagrams. However, the present invention is notrestricted to the embodiments and the examples described below. Thesingle-focus optical system means an optical system having a singlefocal length.

A single-focus optical system of the present embodiment is asingle-focus optical system which forms a conjugate relationship betweena conjugate point on an enlargement side at a long distance and aconjugate point of a reduction side at a short distance, and includes inorder from the enlargement side, a first lens unit, and a second lensunit having a positive refractive power. A lens component is one of asingle lens and a cemented lens. The first lens unit includes areduction-side negative lens component closest to the reduction side,and in addition, the first lens unit includes not less than threenegative lens components including the reduction-side negative lenscomponent. The second lens unit includes in order from the enlargementside, a first positive lens, a second positive lens, a first negativelens, and a third positive lens, and all air spaces in the second lensunit are constant at a time of focusing.

The single-focus optical system of the present embodiment is based on anErnostar type optical system or a Sonnar type optical system, or anoptical system of a type having an arrangement conforming to theErnostar type optical system or the Sonnar type optical system, and hasa high-performance afocal system with an angular magnification less than1, added to an enlargement side of a lens system on which it is based.Since a preferable refractive power in the afocal system is to beroughly zero, the afocal system may have some positive refractive poweror negative refractive power.

By making such arrangement, it is possible to correct particularly aspherical aberration, a coma, a longitudinal chromatic aberration, and achromatic aberration of magnification extremely favorably. As a result,it is possible to realize a single-focus optical system having animaging performance higher than an imaging performance by theconventional Gaussian type optical system. For instance, in asingle-focus optical system, it is possible to secure an F-numbersmaller than 1.4, and an angle of view not smaller than 50°.

In this way, according to the single-focus optical system of the presentembodiment, it is possible to provide a single-focus optical systemwhich has an F-number smaller than 1.4 in a category of lenses from astandard lens to a wide-angle lens, and has an extremely high potentialfor aberration correction. Particularly, regarding the imagingperformance, it is possible to have imaging performance of a level farsuperior to that of a conventional single-focus optical system for a35mm film size.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the second positive lens and the first negativelens be cemented mutually.

By making such arrangement, it is possible to correct the longitudinalchromatic aberration and the chromatic aberration of magnification in abalanced manner.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the secondsub-unit include only a negative lens component.

In an optical system having a large aperture ratio, the sphericalaberration, the coma, and an astigmatism in particular, are strictlysought to be corrected favorably. Therefore, by making such arrangement,even when the spherical aberration, the coma, and the astigmatism haveremained in the first sub-unit, it is possible to cancel in the secondsub-unit almost all the aberrations remained. In this case, even whenthe second sub-unit includes a fewer number of lenses, it is possible tocorrect in the second sub-unit the aberration remained in the firstsub-unit.

Or, when carrying out inner focusing is taken into consideration, it ispossible to make a lens to be moved light-weight, by moving the negativelens component along the optical axis. As a result, a focusing with ahigh speed and extremely small aberration fluctuation also becomespossible.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the secondsub-unit include only a negative lens component, and the second sub-unitinclude a negative lens component of a meniscus shape having a concavesurface directed toward the reduction side.

In an optical system having a large aperture ratio, the sphericalaberration, the coma, and an astigmatism in particular, are strictlysought to be corrected favorably. Therefore, by making such arrangement,even when the spherical aberration, the coma, and the astigmatism haveremained in the first sub-unit, it is possible to cancel in the secondsub-unit almost all the aberrations remained. In this case, even whenthe second sub-unit includes a fewer number of lenses, it is possible tocorrect in the second sub-unit the aberration remained in the firstsub-unit.

Or, when carrying out inner focusing is taken into consideration, it ispossible to make a lens to be moved light-weight, by moving the negativelens component along the optical axis. As a result, a focusing with ahigh speed and extremely small aberration fluctuation also becomespossible.

Furthermore, by letting the shape of the negative lens component in thesecond sub-unit to be the meniscus shape having a concave surfacedirected toward the reduction side, even in a case in which the apertureratio is made further larger, or the angle of view is made furtherwider, it is possible to correct each aberration favorably.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the secondsub-unit include only a negative lens component, and focusing be carriedout by moving the second sub-unit on an optical axis.

In an optical system having a large aperture ratio, the sphericalaberration, the coma, and an astigmatism in particular, are strictlysought to be corrected favorably. Therefore, by making such arrangement,even when the spherical aberration, the coma, and the astigmatism haveremained in the first sub-unit, it is possible to cancel in the secondsub-unit almost all the aberrations remained. In this case, even whenthe second sub-unit includes a fewer number of lenses, it is possible tocorrect in the second sub-unit the aberration remained in the firstsub-unit.

Or, when carrying out inner focusing is taken into consideration, bymoving the negative lens component along the optical axis, a focusingwith extremely small aberration fluctuation becomes possible. Moreover,since it is possible to make the lens to be moved light-weight, it ispossible to reduce a load on a drive mechanism. As a result, focusingwith a high speed is possible.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include a reduction-side positive lens component closest to thereduction side, and the second sub-unit include only a negative lenscomponent.

By making such arrangement, even in a case in which the aperture ratiois made further larger, and the angle of view is widened further, it ispossible to correct favorably the spherical aberration, the coma, theastigmatism, and a curvature of field, and in addition, the longitudinalchromatic aberration and the chromatic aberration of magnification,while securing an adequate back focus.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and the second sub-unit, and thesecond sub-unit include only a negative lens component, and at the timeof focusing, a distance between the first sub-unit and the secondsub-unit, and a distance between the second sub-unit and the second lensunit change.

In an optical system having a large aperture ratio, in particular, thespherical aberration, the coma, and the astigmatism are strictly soughtto be corrected favorably. Therefore, by making such arrangement, afocusing with an extremely small aberration fluctuation is possible.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first sub-unit and the second lens unit befixed at the time of focusing.

By making such arrangement, it is possible to make small the number oflens units to be moved at the time of focusing, and focusing with anextremely small aberration fluctuation becomes possible.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include an enlargement-side lens component closest to theenlargement side, and the enlargement-side lens component be a negativesingle lens, and the second sub-unit include only a negative lenscomponent.

By making such arrangement, it is possible to prevent the first lensunit from becoming large-sized even when an angle is widened in theoptical system.

Moreover, in the single-focus optical of the present embodiment, it ispreferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include a cemented lens, and the cemented lens in the firstsub-unit include in order from the enlargement side, a negative lens anda positive lens, and a shape of the cemented lens in the first sub-unitbe a meniscus shape having a concave surface directed toward theenlargement side, and the second sub-unit include only a negative lenscomponent.

By making such arrangement, it is possible to correct favorably, thespherical aberration, the coma, an astigmatism, and the curvature offield, and in addition, the longitudinal chromatic aberration and thechromatic aberration of magnification.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include a cemented lens and a reduction-side lens component,and the cemented lens in the first sub-unit include in order from theenlargement side, a negative lens and a positive lens, and a shape ofthe cemented lens in the first sub-unit be a meniscus shape having aconcave surface directed toward the enlargement side, and thereduction-side lens component be disposed adjacent to the cemented lensin the first sub-unit, on the enlargement side of the cemented lens inthe first sub-unit, and a shape of the reduction-side lens component bea meniscus shape having a convex surface directed toward the enlargementside, and the second sub-unit include only a negative lens component.

By making such arrangement, even in a case in which the aperture ratiois made further larger, and the angle of view is widened further, it ispossible to correct favorably the spherical aberration, the coma, theastigmatism, and a curvature of field, and in addition, the longitudinalchromatic aberration and the chromatic aberration of magnification.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the secondsub-unit include only one negative lens component.

In an optical system having a large aperture ratio, the sphericalaberration, the coma, and an astigmatism in particular, are strictlysought to be corrected favorably. Therefore, by making such arrangement,even when the spherical aberration, the coma, and the astigmatism haveremained in the first sub-unit, it is possible to cancel in the secondsub-unit almost all the aberrations remained. In this case, even whenthe second sub-unit includes a fewer number of lenses, it is possible tocorrect in the second sub-unit the aberration remained in the firstsub-unit. As a result, it is possible to correct the sphericalaberration, the coma, and the astigmatism in a balanced manner as awhole.

Or, when carrying out inner focusing is taken into consideration, bymoving the second sub-unit along the optical axis, a focusing withextremely small aberration fluctuation becomes possible. Moreover, sinceit is possible to make the lens to be moved light-weight, it is possibleto reduce a load on a drive mechanism. As a result, focusing with a highspeed is possible.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include in order from the enlargement side, a cemented lens,and a plurality of positive lens components, and the plurality ofpositive lens components include all positive lens components that areadjacent, and the cemented lens unit in the first sub-unit include inorder from the enlargement side, a negative lens and a positive lens,and a shape of the cemented lens in the first sub-unit be a meniscusshape having a concave surface directed toward the enlargement side, andthe second sub-unit include only a negative lens component.

By making such arrangement, even in a case in which the aperture ratiois made further larger, and the angle of view is widened further, it ispossible to correct favorably the spherical aberration, the coma, theastigmatism, and a curvature of field, and in addition, the longitudinalchromatic aberration and the chromatic aberration of magnification,while securing an adequate back focus.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the following conditional expression (1) besatisfied:

0.75<SF₁₁<3.5   (1)

where,

SF₁₁=(R_(F11)+R_(R11))/(R_(F11)−R_(R11)), and here

R_(F11) denotes a radius of curvature of an enlargement-side surface ofthe enlargement-side lens component, and

R_(R11) denotes a radius of curvature of a reduction-side surface of theenlargement-side lens component.

By making so as not to exceed an upper limit value of conditionalexpression (1), in particular, correction of the astigmatism becomeseasy. By making so as not to fall below a lower limit value ofconditional expression (1), in particular, correction of a barreldistortion becomes easy.

Here, it is more preferable that the following conditional expression(1′) be satisfied instead of conditional expression (1).

0.85<SF₁₁<3.0   (1′)

Moreover, it is even more preferable that the following conditionalexpression (1″) be satisfied instead of conditional expression (1).

0.95<SF₁₁<2.7   (1″)

Moreover, it is preferable that the single-focus optical system of thepresent embodiment include a reduction-side lens component on theenlargement side of the cemented lens in the first sub-unit, and a shapeof the reduction-side lens component be a meniscus shape having a convexsurface directed toward the enlargement side, and the followingconditional expression (2) be satisfied:

1.4<SF₁₂<15   (2)

where,

SF₁₂=(R_(F12)+R_(R12))/(R_(F12)−R_(R12)), and here

R_(F12) denotes a radius of curvature of an enlargement-side surface ofthe reduction-side lens component, and

R_(R12) denotes a radius of curvature of a reduction-side surface of thereduction-side lens component.

By making so as not to exceed either an upper limit value of conditionalexpression (2), or so as not to fall below a lower limit value ofconditional expression (2), it becomes easy to correct the sphericalaberration and the coma in a balanced manner even when the apertureratio is made large as well as the angle of view is widened.

Here, it is more preferable that the following conditional expression(2′) be satisfied instead of conditional expression (2).

1.6<SF₁₂<10   (2′)

Moreover, it is even more preferable that the following conditionalexpression (2″) be satisfied instead of conditional expression (2).

1.8<SF₁₂<8.0   (2″)

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the following conditional expression (3) besatisfied:

−15<SF ₁₃<−2.0   (3)

where,

SF₁₃=(R_(F13)+R_(R13))/(R_(F3)−R_(R13)), and here

R_(F13) denotes a radius of curvature of an enlargement-side surface ofthe cemented lens in the first sub-unit, and

R_(R13) denotes a radius of curvature of a reduction-side surface of thecemented lens in the first sub-unit.

By making so as not to exceed either an upper limit value of conditionalexpression (3), or so as not to fall below a lower limit value ofconditional expression (3), it becomes easy to correct the sphericalaberration and the coma in a balanced manner even when the apertureratio is made large as well as the angle of view is widened.

Here, it is more preferable that the following conditional expression(3′) be satisfied instead of conditional expression (3).

−12<SF ₁₃<−2.5   (3′)

Moreover, it is even more preferable that the following conditionalexpression (3″) be satisfied instead of conditional expression (3).

−10<SF ₁₃<−3.0   (3″)

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the plurality of positive lens components includea front-side positive lens component which is positioned closest to theenlargement side, and a rear-side positive lens component which ispositioned closest to the reduction side, and the following conditionalexpression (4) be satisfied:

0.10<SF ₁₄ −SF ₁₅<7.0   (4)

where,

SF₁₄=(R_(F14)+R_(R14))/(R_(F14)−R_(R14)) , and

SF₁₅=(R_(F15)+R_(R15))/(R_(F15)−R_(R15)) , and here

R_(F14) denotes a radius of curvature of an enlargement-side surface ofthe front-side positive lens component,

R_(R14) denotes a radius of curvature of a reduction-side surface of thefront-side positive lens component,

R_(F15) denotes a radius of curvature of an enlargement-side surface ofthe rear-side positive lens component, and

R_(R15) denotes a radius of curvature of a reduction-side surface of therear-side positive lens component.

In the first lens unit, at positions where the plurality of positivelens components is disposed, a height of an axial light ray is high.Consequently, a shape of each lens component in the plurality ofpositive lens components has a close connection with the correction ofthe spherical aberration which has an effect on a sharpness of anoverall image.

Moreover, an axial light beam is in a diverged state at the enlargementside of the plurality of positive lens components. In the plurality ofpositive lens components, for turning the diverged state to a convergedstate, it is preferable to arrange each positive lens component suchthat a shaping factor of each positive lens component assumes a negativedirection from the enlargement side to the reduction side. Moreover, itis necessary that a difference in the shaping factor of the positivelens components positioned at two ends out of the plurality of positivelens components assumes an appropriate value.

By making so as not to exceed either an upper limit value of conditionalexpression (4), or so as not to fall below a lower limit value ofconditional expression (4), the correction of the spherical aberrationbecomes easy even when the aperture ratio is made large as well as theangle of view is widened.

Here, it is more preferable that the following conditional expression(4′) be satisfied instead of conditional expression (4).

0.30<SF ₁₄ −SF ₁₅<6.0   (4′)

Moreover, it is even more preferable that the following conditionalexpression (4″) be satisfied instead of conditional expression (4).

0.45<SF ₁₄ −SF ₁₅<5.5   (4″)

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the second sub-unit include only one negative lenscomponent, and the following conditional expression (5) be satisfied:

0.80<SF₁₆<4.0   (5)

where,

SF₁₆=(R_(F16)+R_(R16))/(R_(F16)−R_(R16)) , and here

R_(F16) denotes a radius of curvature of an enlargement-side surface ofthe negative lens component in the second sub-unit, and

R_(R16) denotes a radius of curvature of a reduction-side surface of thenegative lens component in the second sub-unit.

In a case of using the inner focusing, the fluctuation in aberrationbecomes a problem. In the inner focusing, when the second sub-unit islet to be a unit that moves on the optical axis, it is possible tominimize the fluctuation in aberration. Therefore, it is possible tocarry out stable focusing. Furthermore, by satisfying conditionalexpression (5), it is possible to suppress adequately the fluctuation inaberration.

By making so as not to exceed an upper limit value of conditionalexpression (5), it is possible to suppress an increase in thefluctuation of astigmatism. By making so as not to fall below a lowerlimit value of conditional expression (5), it is possible to suppressthe fluctuation in the spherical aberration.

Here, it is more preferable that the following conditional expression(5′) be satisfied instead of conditional expression (5).

0.85<SF₁₆<3.0   (5′)

Moreover, it is even more preferable that the following conditionalexpression (5″) be satisfied instead of conditional expression (5).

0.90<SF₁₆<2.5   (5″)

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include in order from theenlargement side, a first sub-unit and a second sub-unit, and the firstsub-unit include a reduction-side positive lens component closest to thereduction side, and the reduction-side positive lens component be apositive single lens, and the second sub-unit include only a negativelens component, and in a rectangular coordinate system in which ahorizontal axis is let to be Nd_(1PR) and a vertical axis is let to bevd_(1PR), when a straight line represented byNd_(1PR)=α×vd_(1PR)+β_(1PR), where, α=−0.01, Nd_(1PR) and vd_(1PR) forthe reduction-side positive lens component be included in both of anarea determined by a straight line when a lower limit value of a rangeof the following conditional expression (11) is β_(1PR)=2.25, and anarea determined by the following conditional expressions (12) and (13):

2.25≦β_(1PR)   (11),

1.40<Nd_(1PR)   (12) , and

35<vd_(1PR)   (13)

where,

Nd_(1PR) denotes a refractive index of the reduction-side positive lenscomponent, and

vd_(1PR) denotes Abbe number for the reduction-side positive lenscomponent.

In the first sub-unit, at positions where the plurality of positive lenscomponents is disposed, the height of the axial light ray is high.Consequently, in the plurality of positive lens components, particularlya chromatic aberration such as the longitudinal chromatic aberration andthe spherical aberration is susceptible to occur.

The reduction-side lens component is disposed closest to the reductionside in the first sub-unit. This position is a position which isfarthest away from the cemented lens in the first sub-unit.

For small-sizing and light-weighting of the first lens unit, it ispreferable to include a single lens in the reduction-side positive lenscomponent. However, at the position where the reduction-side positivelens component is disposed, the chromatic aberration is susceptible tooccur as mentioned above. Therefore, in a case of including a singlelens in the reduction-side positive lens component, an arrangement is tobe made such that the refractive index and Abbe number for thereduction-side positive lens component is included in the areadetermined by conditional expressions (11), (12), and (13) . By makingsuch arrangement, it is possible to suppress an occurrence of achromatic aberration such as the longitudinal chromatic aberration andthe spherical aberration.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the second sub-unit include one negative lenscomponent, and the negative lens component in the second sub-unit be asingle lens, and in a rectangular coordinate system in which ahorizontal axis is let to be Nd_(1NR) and a vertical axis is let to bevd_(1NR), when a straight lien represented byNd_(1NR)=α×vd_(1NR)+β_(1NR), where, α=−0.01, Nd_(1NR) and vd_(1NR) forthe negative lens component in the second sub-unit be included in bothof an area determined by a straight line when a lower limit value of arange of the following conditional expression (14) is β_(1NR)=2.15, andan area determined by the following conditional expressions (15) and(16):

2.15≦β_(1NR)   (14),

1.45<Nd_(1NR)   (15) , and

25<v_(1NR) (16)

where,

Nd_(1NR) denotes a refractive index of the negative lens component inthe second sub-unit, and vd_(1NR) denotes Abbe number for the negativelens component in the second sub-unit.

In a case of moving the second sub-unit at the time of focusing, thefluctuation in the chromatic aberration is desired to be small. Anarrangement is to be made such that the refractive index and Abbe numberfor the negative lens component in the second sub-unit is included in anarea determined by conditional expressions (14), (15), and (16). Bymaking such arrangement, it is possible to suppress an occurrence of achromatic aberration such as the longitudinal chromatic aberration, thechromatic aberration of magnification, the spherical aberration, or achromatic coma.

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the first lens unit include an enlargement-sidelens component closest to the enlargement side, and the followingconditional expression (A) be satisfied:

0<f/e _(N1F)<2   (A)

where,

f denotes the focal length of the overall single-focus optical system atthe time of focusing to an object at infinity, and

e_(N1F) denotes a maximum effective aperture of the enlargement-sidelens component in the first lens unit.

In a case of exceeding an upper limit value of conditional expression(A), it becomes difficult to widen the angle of view. In other words,when an attempt is made to widen the angle of view, the sphericalaberration, the distortion, and the astigmatism are susceptible tooccur. On the other hand, In a case of falling below a lower limit valueof conditional expression (A), the optical system is susceptible tobecome large-sized in a radial direction.

Here, it is preferable that the following conditional expression (A′) besatisfied instead of conditional expression (A).

0.1<f/e _(N1F)<1.5   (A′)

Moreover, it is even more preferable that the following conditionalexpression (A″) be satisfied instead of conditional expression (A).

0.2<f/e _(N1F)<1   (A″)

Moreover, it is preferable that the single-focus optical system of thepresent embodiment include an aperture stop, and the followingconditional expression (B) be satisfied:

0<(f/e _(AS))/Fno<2   (B)

where,

f denotes the focal length of the overall single-focus optical system atthe time of focusing to an object at infinity,

e_(AS) denotes a maximum diameter of the aperture stop, and

Fno denotes an F-number for the overall single-focus optical system atthe time of focusing to an object at infinity.

In a case of exceeding upper limit value of conditional expression (B),it becomes difficult to widen the angle of view. In other words, when anattempt is made to widen the angle of view, correction of the sphericalaberration and the chromatic aberration becomes difficult. Whereas, In acase of falling below a lower limit value of conditional expression (B),the optical system is susceptible to become large-sized in the radialdirection.

Here, it is more preferable that the following conditional expression(B′) be satisfied instead of conditional expression (B).

0.2<(f/e _(AS))/Fno<1   (B′) Moreover, it is more preferable that thefollowing conditional expression (B″) be satisfied instead ofconditional expression (B).

0.3<(f/e _(AS))/Fno<0.9   (B″)

Moreover, in the single-focus optical system of the present embodiment,it is preferable that the following conditional expression (C) besatisfied:

0<T _(air) _(_) _(max) /Σd≦0.27   (C)

where,

Tair_(air) _(_) _(max) is a largest axial air space in the range from asurface positioned closest to the enlargement side to a surfacepositioned closest to the reduction side in the single-focus opticalsystem, and

Σd is an axial distance from the surface positioned closest to theenlargement side to the surface positioned closest to the reduction sidein the single-focus optical system.

Conditional expression (C) is a conditional expression which isadvantageous for securing a high optical performance, shortening theoverall length of the optical system, and making small an outer diameterof the image forming optical system.

Widening appropriately an air space between the lenses leads to animprovement in an optical performance. However, securing an opticalperformance by widening excessively the air space between the lenseswith respect to Σd, that is, the axial distance from the lens surfacepositioned closest to the enlargement side up to a lens surfacepositioned closest to the reduction side of the single-focus opticalsystem, may lead to an increase in the overall length of the opticalsystem and making an aperture of the optical system large.

Therefore, satisfying conditional expression (C) is advantageous forsecuring the number of lenses necessary for realizing a high opticalperformance while shortening the overall length of the optical system,and making the aperture small.

Here, it is more preferable that the following conditional expression(C′) be satisfied instead of conditional expression (C).

0.03<T _(air) _(_) _(max) /Σd≦0.2   (C′)

Moreover, it is even more preferable that the following conditionalexpression (C″) be satisfied instead of conditional expression (C).

0.07<T _(air) _(_) _(max) /Σd≦0.18   (C″)

Moreover, an optical apparatus of the present embodiment includes anoptical system and an image pickup element which is disposed on areduction side. The image pickup element has an image pickup surface,and converts an image formed on the image pickup surface by the opticalsystem to an electric signal, and the optical system is theabovementioned single-focus optical system.

According to the optical apparatus of the present embodiment, it ispossible to pick up an image with a wide photographing range, a lownoise, and a high resolution.

Moreover, an optical apparatus of the present embodiment includes anoptical system, and a display element which is disposed on the reductionside. The display element has a display surface, and an image displayedon the display surface is projected on the enlargement side by theoptical system, and the optical system is the abovementionedsingle-focus optical system.

According to the optical apparatus of the present embodiment, it ispossible to project an image with a wide projection range, a low noise,and a high resolution.

The abovementioned single-focus optical system and the optical apparatusmay satisfy a plurality of arrangements simultaneously. Making sucharrangement is preferable for achieving a favorable single-focus opticalsystem and optical apparatus. Moreover, combinations of preferablearrangements are arbitrary. For each conditional expression, only theupper limit value or the lower limit value of a numerical range of aconditional expression further restricted, may be limited.

Examples of the single-focus optical system will be described below indetail by referring to the accompanying diagrams. However, the presentinvention is not restricted to the examples described below.

Examples 1 to 4 of the single-focus optical system will be describedbelow by referring to the accompanying diagrams. Each of single-focusoptical systems in examples 1 to 4 is a single-focus optical system withan F-number less than 1.5.

FIG. 1A, FIG. 2A, FIG. 3A, and FIG. 4A show lens cross-sectional viewsfor the single-focus optical systems of the examples. The lenscross-sectional views are lens cross-sectional views at the time offocusing to an object at infinity.

FIG. 1B, FIG. 2B, FIG. 3B, and FIG. 4B show a spherical aberration (SA)in the single-focus optical systems of the examples.

FIG. 1C, FIG. 2C, FIG. 3C, and FIG. 4C show an astigmatism (AS) in thesingle-focus optical systems of the examples.

FIG. 1D, FIG. 2D, FIG. 3D, and FIG. 4D show a distortion (DT) in thesingle-focus optical systems of the examples.

FIG. 1E, FIG. 2E, FIG. 3E, and FIG. 4E show a chromatic aberration ofmagnification in the single-focus optical systems of the examples. Eachaberration diagram is an aberration diagram at the time of focusing toan object at infinity. Moreover, ω denotes a half angle of view.

Moreover, in the lens cross-sectional view of each example, a first lensunit is denoted by G1, a second lens unit is denoted by G2, a coverglass is denoted by C, and an image plane is denoted by I.

Although it is not shown in the diagrams, a plane parallel plate whichforms a low-pass filter may be disposed between the second lens unit G2and the image plane I. A wavelength-region restricting coating whichrestricts infra-red rays may be applied to a surface of the planeparallel plate. Moreover, a multilayer film for wavelength-regionrestriction may be applied to a surface of the cover glass. Furthermore,the cover glass C may be imparted with an effect of a low-pass filter.

Moreover, in a case of using the single-focus optical system for imagepickup, an image pickup element is disposed on the image plane I.Whereas, in a case of using the single-focus optical system forprojection, a display element is disposed on the image plane I. In thedescription of an arrangement of each example, the description will bemade assuming that the single-focus optical system is used for imagepickup. Therefore, the enlargement side will be let to be an objectside, and the reduction side will be let to be an image side.

A single-focus optical system according to an example 1 will bedescribed below.

The single-focus optical system according to the example 1 includes inorder from an object side, a first lens unit G1 having a positiverefractive power and a second lens unit G2 having a positive refractivepower. The first lens unit G1 includes an aperture stop S.

The first lens unit G1 includes a first sub-unit and a second sub-unit.The first sub-unit includes a negative meniscus lens L1 having a convexsurface directed toward the object side, a negative meniscus lens L2having a convex surface directed toward the object side, a biconvexpositive lens L3, a biconcave negative lens L4, a biconcave negativelens L5, a biconvex positive lens L6, a biconvex positive lens L7, and apositive meniscus lens L8 having a convex surface directed toward theobject side. The second sub-unit includes a negative meniscus lens L9having a convex surface directed toward the object side. Here, thebiconvex positive lens L3 and the biconcave negative lens L4 arecemented. The biconcave negative lens L5 and the biconvex positive lensL6 are cemented.

The second lens unit G2 includes a biconvex positive lens L10, abiconvex positive lens L11, a biconcave negative lens L12, and apositive meniscus lens L13 having a convex surface directed toward theobject side. Here, the biconvex positive lens L11 and the biconcavenegative lens L12 are cemented.

Moreover, at the time of focusing from an object at infinity to anobject at a close distance, the negative meniscus lens L9 moves towardan image side along an optical axis.

An aspherical surface is provided to a total of four surfaces which are,both surfaces of the negative meniscus lens L2 and both surfaces of thenegative meniscus les L9.

Next, a single-focus optical system according to an example 2 will bedescribed below.

The single-focus optical system according to the example 5 includes inorder from an object side, a first lens unit G1 having a positiverefractive power and a second lens unit G2 having a positive refractivepower. The first lens unit G1 includes an aperture stop S.

The first lens unit G1 includes a first sub-unit and a second sub-unit.The first sub-unit includes a negative meniscus lens L1 having a convexsurface directed toward the object side, a negative meniscus lens L2having a convex surface directed toward the object side, a biconvexpositive lens L3, a biconcave negative lens L4, a biconcave negativelens L5, a biconvex positive lens L6, a biconvex positive lens L7, and apositive meniscus lens L8 having a convex surface directed toward theobject side. The second sub-unit includes a negative meniscus lens L9having a convex surface directed toward the object side. Here, thebiconvex positive lens L3 and the biconcave negative lens L4 arecemented. Moreover, the biconcave negative lens L5 and the biconvexpositive lens L6 are cemented.

The second lens unit G2 includes a biconvex positive lens L10, abiconvex positive lens L11, a biconcave negative lens L12, and apositive meniscus lens L13 having a convex surface directed toward theobject side. Here, the biconvex positive lens L11 and the biconcavenegative lens L12 are cemented.

Moreover, at the time of focusing from an object at infinity to anobject at a close distance, the negative meniscus lens L9 moves towardan image side along an optical axis.

An aspherical surface is provided to a total of four surfaces which are,both surfaces of the negative meniscus lens L2 and both surfaces of thenegative meniscus lens L9.

Next, a single-focus optical system according to an example 3 will bedescribed below.

The single-focus optical system according to the example 6 includes inorder from an object side, a first lens unit G1 having a positiverefractive power and a second lens unit G2 having a positive refractivepower. The first lens unit G1 includes an aperture stop S.

The first lens unit G1 includes a first sub-unit and a second sub-unit.The first sub-unit includes a negative meniscus lens L1 having a convexsurface directed toward the object side, a negative meniscus lens L2having a convex surface directed toward the object side, a biconvexpositive lens L3, a biconcave negative lens L4, a biconcave negativelens L5, a biconvex positive lens L6, a biconvex positive lens L7, and abiconvex positive lens L8. The second sub-unit includes a negativemeniscus lens L9 having a convex surface directed toward the objectside. Here, the biconvex positive lens L3 and the biconcave negativelens L4 are cemented. Moreover, the biconcave negative lens L5 and thebiconvex positive lens L6 are cemented.

The second lens unit G2 includes a biconvex positive lens L10, abiconvex positive lens L11, a biconcave negative lens L12, and apositive meniscus lens L13 having a convex surface directed toward theobject side. Here, the biconvex positive lens L11 and the biconcavenegative lens L12 are cemented.

Moreover, at the time of focusing from an object at infinity to anobject at a close distance, the negative meniscus lens L9 moves towardan image side along an optical axis.

An aspherical surface is provided to a total of four surfaces which are,both surfaces of the negative meniscus lens L2 and both surfaces of thenegative meniscus lens L9.

Next, a single-focus optical system according to an example 4 will bedescribed below.

The single-focus optical system according to the example 4 includes inorder from an object side, a first lens unit G1 having a positiverefractive power and a second lens unit G2 having a positive refractivepower. The first lens unit G1 includes an aperture stop S.

The first lens unit G1 includes a first sub-unit and a second sub-unit.The first sub-unit includes a negative meniscus lens L1 having a convexsurface directed toward the object side, a positive meniscus lens L2having a convex surface directed toward the object side, a positivemeniscus lens L3 having a convex surface directed toward the objectside, a negative meniscus lens L4 having a convex surface directedtoward the object side, a biconcave negative lens L5, a biconvexpositive lens L6, a biconvex positive lens L7, and a positive meniscuslens L8 having a convex surface directed toward the object side. Thesecond sub-unit includes includes a negative meniscus lens L9 having aconvex surface directed toward the object side. Here, the positivemeniscus lens L3 and the negative meniscus lens L4 are cemented.Moreover, the biconcave negative lens L5 and the biconvex positive lensL6 are cemented.

The second lens unit G2 includes a positive meniscus lens L10 having aconvex surface directed toward an image side, a biconvex positive lensL11, a biconcave negative lens L12, and a biconvex positive lens L13.Here, the biconvex positive lens L11 and the biconcave negative lens L12are cemented.

Moreover, at the time of focusing from an object at infinity to anobject at a close distance, the negative meniscus lens L9 moves towardthe image side along an optical axis.

An aspherical surface is provided to both surfaces of the negativemeniscus lens L9.

Next, numerical data of optical components configuring the single-focusoptical system of each above example are shown. In numerical data ofeach example, r1, r2, . . . denotes a curvature radius of each lenssurface, d1, d2, . . . denotes a thickness of each lens or an airdistance between adjacent lens surfaces, nd1, nd2, . . . denotes arefractive index of each lens for d-line, v1, vd2, . . . denotes an Abbenumber of each lens, * denotes an aspherical surface. Moreover, invarious data, f denotes a focal length of an imaging optical system as awhole, FNO. denotes an F number, ω denotes a half angle of view, IHdenotes an image height, FB denotes a back focus, LTL denotes a lenstotal length. The lens total length is the distance from the frontmostlens surface to the rearmost lens surface plus back focus. The backfocus is a unit which is expressed upon air conversion of a distancefrom the lens backmost surface to a paraxial image surface. Moreover,the unit of angle is ° (degree). Moreover, Infinity indicates the timeof focusing to an object at infinity and Close distance indicates thetime of focusing to an object at a close distance.

A shape of an aspherical surface is defined by the following expressionwhere the direction of the optical axis is represented by z, thedirection orthogonal to the optical axis is represented by y, a conicalcoefficient is represented by K, aspherical surface coefficients arerepresented by A4, A6, A8, A10,

Z=(y ² /r)/[1+{1−(1+k)(y/r)²}^(1/2) ]+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰

Further, in the aspherical surface coefficients, ‘e-n’ (where, n is anintegral number) indicates ‘10^(−n)’. Moreover, these symbols arecommonly used in the following numerical data for each example.

EXAMPLE 1

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 45.9461.50 1.48749 70.23  2 14.406 9.15  3* 130.753 1.20 1.58313 59.38  4*27.135 0.76  5 28.653 6.18 2.00069 25.46  6 −33.821 1.20 1.58144 40.75 7 20.407 5.07  8 −25.734 1.20 1.80518 25.42  9 25.000 6.18 1.6968055.53 10 −35.122 0.20 11 63.389 5.66 1.72916 54.68 12 −31.891 0.7013(Stop) ∞ 0.40 14 35.850 2.94 1.49700 81.61 15 244.348 Variable 16*92.337 1.20 1.85400 40.39 17* 25.577 Variable 18 54.229 4.71 1.5952267.74 19 −43.438 0.20 20 30.927 5.69 2.00100 29.13 21 −89.137 1.201.80518 25.42 22 18.359 1.76 23 36.962 2.79 1.72916 54.68 24 1389.52211.49  25 ∞ 2.66 1.51633 64.14 26 ∞ 1.00 Image plane ∞ Asphericalsurface data 3rd surface k = 0.000 A4 = −1.99067e−05, A6 = 6.32029e−09,A8 = −1.75482e−10 4th surface k = 0.000 A4 = −5.57900e−06, A6 =−7.59483e−09, A8 = −1.60555e−10 16th surface k = 0.000 A4 =−2.38100e−06, A6 = 4.81486e−09, A8 = −7.43803e−14 17th surface k = 0.000A4 = 3.21789e−06, A6 = 3.58266e−09, A8 = 7.48716e−12 Various data f17.27 FNO. 1.29 2ω 72.96 IH 11.15 FB(in air) 14.25 LTL(in air) 86.58Infinity Close distance d15 2.62 6.20 d17 9.83 6.25 Unit focal length f1= 132.31 f2 = 26.68

EXAMPLE 2

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 40.0001.50 1.48749 70.23  2 14.959 10.01   3* 284.838 1.20 1.49700 81.61  4*24.501 1.55  5 30.509 6.26 2.00069 25.46  6 −32.686 1.30 1.58144 40.75 7 22.918 4.80  8 −27.864 1.20 1.85478 24.80  9 25.040 6.47 1.6968055.53 10 −34.741 0.20 11 55.767 5.17 1.72916 54.68 12 −35.759 0.20 1336.555 3.19 1.43875 94.93 14 4229.057 0.62 15(Stop) ∞ Variable 16*112.818 1.20 1.85400 40.39 17* 25.701 Variable 18 70.785 3.81 1.7291654.68 19 −48.006 0.20 20 28.778 5.11 2.00100 29.13 21 −53.599 1.201.85478 24.80 22 18.702 1.95 23 38.612 2.63 1.72916 54.68 24 13210.08711.35  25 ∞ 2.66 1.51633 64.14 26 ∞ 1.00 Image plane ∞ Asphericalsurface data 3rd surface k = 0.000 A4 = −1.98270e−05, A6 = −1.62289e−08,A8 = −6.87416e−11 4th surface k = 0.000 A4 = −4.30732e−06, A6 =−4.24639e−08, A8 = −4.55491e−11 16th surface k = 0.000 A4 =−1.79188e−06, A6 = 1.11638e−10 17th surface k = 0.000 A4 = 3.97297e−06,A6 = −1.99307e−10 Various data f 17.27 FNO. 1.29 2ω 72.65 IH 11.15 FB(inair) 14.11 LTL(in air) 86.46 Infinity Close distance d15 3.41 6.92 d179.16 5.65 Unit focal length f1 = 145.14 f2 = 25.48

EXAMPLE 3

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 1822.4981.50 1.48749 70.23  2 24.046 4.33  3* 104.293 1.20 1.49700 81.61  4*85.426 0.40  5 33.165 6.73 2.00069 25.46  6 −41.379 1.20 1.58144 40.75 7 21.826 6.38  8 −26.782 1.20 1.85478 24.80  9 25.731 7.42 1.6968055.53 10 −36.641 0.20 11 52.705 5.13 1.72916 54.68 12 −51.343 0.20 1346.341 3.42 1.43875 94.93 14 −290.158 0.60 15(Stop) ∞ Variable 16*70.509 1.20 1.74320 49.34 17* 24.442 Variable 18 466.560 3.82 1.7291654.68 19 −36.184 0.20 20 22.789 5.31 2.00100 29.13 21 −224.725 1.201.85478 24.80 22 16.310 2.53 23 40.941 1.79 1.72916 54.68 24 84.29611.94  25 ∞ 2.66 1.51633 64.14 26 ∞ 1.00 Image plane ∞ Asphericalsurface data 3rd surface k = 0.000 A4 = −1.20042e−05, A6 = 2.38213e−09,A8 = −2.73467e−12 4th surface k = 0.000 A4 = −5.23359e−07, A6 =7.45881e−09, A8 = 1.61344e−11 16th surface k = 0.000 A4 = −1.14003e−05,A6 = 1.53037e−08 17th surface k = 0.000 A4 = −7.07063e−06, A6 =7.53398e−09 Various data f 24.59 FNO. 1.29 2ω 51.63 IH 11.15 FB(in air)14.70 LTL(in air) 86.58 Infinity Close distance d15 3.40 9.24 d17 12.536.69 Unit focal length f1 = 119.93 f2 = 31.32

EXAMPLE 4

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 848.6361.50 1.48749 70.23  2 26.057 1.34  3 30.008 4.14 2.00100 29.13  4 79.1520.40  5 31.332 3.61 2.00069 25.46  6 72.289 1.50 1.58144 40.75  7 14.57110.23   8 −26.712 1.50 1.85478 24.80  9 34.227 8.21 1.69680 55.53 10−37.482 0.20 11 52.231 5.56 1.69680 55.53 12 −44.033 0.20 13 30.054 3.961.43875 94.93 14 169.005 1.03 15(Stop) ∞ Variable 16* 1643.120 1.201.74320 49.34 17* 24.933 Variable 18 −933.181 3.97 1.72916 54.68 19−31.002 0.20 20 22.554 5.95 2.00100 29.13 21 −178.529 1.20 1.85478 24.8022 17.042 2.82 23 59.139 2.97 1.72916 54.68 24 −698.477 11.56  25 ∞ 2.661.51633 64.14 26 ∞ 1.00 Image plane ∞ Aspherical surface data 16thsurface k = 0.000 A4 = −1.06473e−05, A6 = 2.88989e−08, A8 = −8.90399e−1217th surface k = 0.000 A4 = −2.82395e−06, A6 = 9.74767e−09, A8 =1.85663e−12 Various data f 25.77 FNO. 1.29 2ω 48.87 IH 11.15 FB(in air)14.31 LTL(in air) 88.04 Infinity Close distance d15 2.90 7.95 d17 9.154.10 Unit focal length f1 = 515.10 f2 = 25.80

Next, values of conditional expressions (1) to (5), (11) to (16), and(A) to (C) in each example are given below. ‘-’ (hyphen) indicates thatthere is no corresponding arrangement.

Conditional expression Example1 Example2 Example3 (1)SF₁₁ 1.913 2.1951.027 (2)SF₁₂ 5.950 7.039 4.850 (3)SF₁₃ −6.483 −9.103 −6.433 (4)SF₁₄ −SF₁₅ 1.674 1.236 0.738 (5)SF₁₆ 1.766 1.590 2.061 (11)β_(1PR) 2.313 2.3882.388 (12)Nd_(1PR) 1.497 1.43875 1.43875 (13)νd_(1PR) 81.61 94.93 94.93(14)β_(1NR) 2.258 2.258 2.276 (15)Nd_(1NR) 1.854 1.854 1.72916(16)νd_(1NR) 40.39 40.39 54.68 (A)f/e_(N1F) 0.5423631 0.52181270.7857366 (B)(f/e_(AS))/Fno 0.5729585 0.6086666 0.7636523 (C)T_(air)_(—) _(max)/Σd 0.1359051 0.1383453 0.1743081

Conditional expression Example4 (1)SF₁₁ 1.063 (2)SF₁₂ 2.739 (3)SF₁₃−5.960 (4)SF₁₄ − SF₁₅ 1.518 (5)SF₁₆ 1.031 (11)β_(1PR) 2.388 (12)Nd_(1PR)1.43875 (13)νd_(1PR) 94.93 (14)β_(1NR) 2.237 (15)Nd_(1NR) 1.7432(16)νd_(1NR) 49.34 (A)f/e_(N1F) 0.7343145 (B)(f/e_(AS))/Fno 0.8667391(C)T_(air) _(—) _(max)/Σd 0.1388118

The optical apparatus of the present embodiment includes an image pickupapparatus and a projection apparatus. Concrete examples of the imagepickup apparatus and the projection apparatus will be described below.

FIG. 5 is a cross-sectional view of a single-lens mirrorless camera asan electronic image pickup apparatus. In FIG. 5, a photographic opticalsystem 2 is disposed inside a lens barrel of a single-lens mirrorlesscamera 1. A mount portion 3 enables the photographic optical system 2 tobe detachable from a body of the single-lens mirrorless camera 1. As themount portion 3, a mount such as a screw-type mount and a bayonet-typemount is to be used. In this example, a bayonet-type mount is used.Moreover, an image pickup element surface 4 and a back monitor 5 aredisposed in the body of the single-lens mirrorless camera 1. As an imagepickup element, an element such as a small-size CCD (charge coupleddevice) or a CMOS (complementary metal-oxide semiconductor) is to beused.

Moreover, as the photographic optical system 2 of the single-lensmirrorless camera 1, the single-focus optical system described in anyone of the examples from the first example to the fourth example is tobe used.

FIG. 6 and FIG. 7 are conceptual diagrams of an arrangement of the imagepickup apparatus. FIG. 6 is a front perspective view showing anappearance of a single-lens mirrorless camera 40 as the image pickupapparatus, and FIG. 7 is a rear perspective view of the single-lensmirrorless camera 40. The single-focus optical system according to thepresent examples from the first example to the fourth example is used ina photographic optical system 41 of the single-lens mirrorless camera40.

The single-lens mirrorless camera40 according to the present embodimentincludes the photographic optical system 41 which is positioned in aphotographic optical path 42, a shutter button 45, and a liquid-crystaldisplay monitor 47. As the shutter button 45 disposed on an upperportion of the single-lens mirrorless camera 40 is pressed, inconjunction with the pressing of the shutter button 45, photography iscarried out by the photographic optical system 41 such as thesingle-focus optical system according to the first example. An objectimage which is formed by the photographic optical system is formed on animage pickup element (photoelectric conversion surface) which isprovided near an image forming surface. The object image which has beenreceived optically by the image pickup element is displayed on theliquid-crystal display monitor 47 which is provided to a rear surface ofthe camera, as an electronic image by a processing means. Moreover, itis possible to record the electronic image which has been photographed,in a storage means.

FIG. 8 is a structural block diagram of an internal circuit of maincomponents of the single-lens mirrorless camera 40. In the followingdescription, the processing means described above includes for instance,a CDS/ADC section 24, a temporary storage memory 117, and an imageprocessing section 18, and a storage means consists of a storage mediumsection 19 for example.

As shown in FIG. 8, the single-lens mirrorless camera 40 includes anoperating section 12, a control section 13 which is connected to theoperating section 12, the temporary storage memory 17 and an imagingdrive circuit 16 which are connected to a control-signal output port ofthe control section 13, via a bus 14 and a bus 15, the image processingsection 18, the storage medium section 19, a display section 20, and aset-information storage memory section 21.

The temporary storage memory 17, the image processing section 18, thestorage medium section 19, the display section 20, and theset-information storage memory section 21 are structured to be capableof mutually inputting and outputting data via a bus 22. Moreover, theCCD 49 and the CDS/ADC section 24 are connected to the imaging drivecircuit 16.

The operating section 12 includes various input buttons and switches,and informs the control section 13 of event information which is inputfrom outside (by a user of the single-lens mirrorless camera) via theseinput buttons and switches. The control section 13 is a centralprocessing unit (CPU), and has a built-in computer program memory whichis not shown in the diagram. The control section 13 controls the entiresingle-lens mirrorless camera 40 according to a computer program storedin this computer program memory.

The CCD 49 is driven and controlled by the imaging drive circuit 16, andwhich converts an amount of light for each pixel of the object imageformed by the photographic optical system 41 to an electric signal, andoutputs to the CDS/ADC section 24.

The CDS/ADC section 24 is a circuit which amplifies the electric signalwhich is input from the CCD 49, and carries out analog/digitalconversion, and outputs to the temporary storage memory 17 image rawdata (Bayer data, hereinafter called as ‘RAW data’) which is onlyamplified and converted to digital data.

The temporary storage memory 17 is a buffer which includes an SDRAM(Synchronous Dynamic Random Access Memory) for example, and is a memorydevice which stores temporarily the RAW data which is output from theCDS/ADC section 24. The image processing section 18 is a circuit whichreads the RAW data stored in the temporary storage memory 17, or the RAWdata stored in the storage medium section 19, and carries outelectrically various image-processing including the distortioncorrection, based on image-quality parameters specified by the controlsection 13.

The storage medium section 19 is a recording medium in the form of acard or a stick including a flash memory for instance, detachablymounted. The storage medium section 19 records and maintains the RAWdata transferred from the temporary storage memory 17 and image datasubjected to image processing in the image processing section 18 in thecard flash memory and the stick flash memory.

The display section 20 includes the liquid-crystal display monitor, anddisplays photographed RAW data, image data and operation menu on theliquid-crystal display monitor. The set-information storage memorysection 21 includes a ROM section in which various image qualityparameters are stored in advance, and a RAM section which stores imagequality parameters which are selected by an input operation on theoperating section 12, from among the image quality parameters which areread from the ROM section.

In the single-lens mirrorless camera 40 configured in such anarrangement, by adopting the single-focus optical system according tothe present invention as the photographic optical system 41, it ispossible to capture an image in a wide photography range with low noiseat high resolution. Moreover, it is possible to use the single-focusoptical system according to the present invention in an image pickupapparatus of a type having a quick-return mirror.

FIG. 9 is a sectional view of a projector as a projection apparatus. Asillustrated in FIG. 9, a projector 100 includes a light source unit 110,an illumination unit 120, an image forming unit 130, and a projectionunit 140.

The light source unit 110 includes a light source 111 and a reflectivemember 112. Illumination light is emitted from the light source 111. Theillumination light is white light. The illumination light is reflectedby the reflective member 112 and enters the illumination unit 120.

The illumination unit 120 includes a first dichroic mirror 121, a seconddichroic mirror 122, a third dichroic mirror 123, a first reflectivemember 124, and a second reflective member 125.

In the first dichroic mirror 121, light in the red wavelength range(hereinafter referred to as “red light”) is transmitted, and light inthe other wavelength ranges is reflected. In the second dichroic mirror122, light in the green wavelength range (hereinafter referred to as“green light”) is reflected, and light in the other wavelength ranges istransmitted. In the third dichroic mirror 123, light in the bluewavelength range (hereinafter referred to as “blue light”) is reflected,and light in the other wavelength ranges is transmitted. The red light,the green light, and the blue light enter the image forming unit 130. Ageneral plane reflector may be used instead of the third dichroic mirror123.

The image forming unit 130 has a first display element 131, a seconddisplay element 132, and a third display element 133.

The first display element 131 is irradiated with red light through thefirst reflective member 124. The second display element 132 isirradiated with green light. The third display element 133 is irradiatedwith blue light through the second reflective member 125.

Here, an identical image is displayed on the first display element 131,the second display element 132, and the third display element 133. Thus,a red image is displayed on the first display element 131, a green imageis displayed on the second display element 132, and a blue image isdisplayed on the third display element 133.

Lights emitted from the first display element 131, the second displayelement 132, and the third display element 133 enter the projection unit140.

The projection unit 140 includes a dichroic prism 141 and a projectionoptical system 142.

Lights emitted from the first display element 131, the second displayelement 132, and the third display element 133 are combined in thedichroic prism 141. As described above, a red image, a green image, anda blue image are displayed in the image forming unit 130. The threeimages are combined by the dichroic prism 141.

The projection optical system 142 projects the combined three images toa predetermined position. For example, the single-focus optical systemillustrated in any one of examples from first examples to fourth exampleabove is used for this projection optical system 142.

The image forming unit 130 may be a light valve such as a digitalmicromirror device (DMD). In this case, light from the light source unit110 is reflected by the light valve, and the image from the light valveis magnified and projected by the projection unit 140.

In the projector 100 thus configured, the single-focus optical systemfocal length lens of the present invention is employed as the projectionoptical system 142, whereby it is possible to project an image in a wideprojection range with low noise at high resolution.

According to the present invention, it is possible to provide asingle-focus optical system in which various aberrations are correctedfavorably, while having a wide angle of view and a small F-number, andan optical apparatus using the same.

As it has been described above, the single-focus optical systemaccording to the present invention is suitable for a single-focusoptical system in which various aberrations are corrected favorably,while having a wide angle of view and a small F-number. Moreover, theoptical apparatus according to the present invention is suitable for animage pickup apparatus which picks up an image over a wide photographingrange, with a low noise, and a high resolution, and for a projectionapparatus which projects an image over a wide projection range, with alow noise, and a high resolution.

1-25 (canceled).
 26. A single-focus optical system which forms aconjugate relationship between a conjugate point on an enlargement sideat a long distance and a conjugate point on a reduction side at a shortdistance, comprising in order from the enlargement side: a first lensunit; and a second lens unit having a positive refractive power,wherein: a lens component is one of a single lens and a cemented lens,and the first lens unit includes a reduction-side negative lenscomponent which is disposed closest to the reduction side, and has aconvex surface on the reduction side, and the first lens unit includes aenlargement-side lens component having a negative refractive power,closest to the enlargement side, and the first lens unit includes acemented lens cemented in order from the enlargement side, a negativelens having concave surface on the enlargement side and a positive lens,and a shape of the cemented lens is a meniscus shape having a concavesurface directed toward the enlargement side, and in addition, the totalnumber of negative lens components in the first lens unit is not lessthan three, and the second lens unit includes in order from theenlargement side, a first positive lens, a second positive lens, a firstnegative lens, and a third positive lens, and all air spaces in thesecond lens unit are constant at a time of focusing.
 27. Thesingle-focus optical system according to claim 26, wherein the secondpositive lens and the first negative lens are cemented mutually.
 28. Thesingle-focus optical system according to claim 26, wherein: the firstlens unit includes in order from the enlargement side, a first sub-unitand a second sub-unit, and all lens components in the second sub-unitinclude negative lens components.
 29. The single-focus optical systemaccording to claim 26, wherein: the first lens unit includes in orderfrom the enlargement side, a first sub-unit and a second sub-unit, andall lens components in the second sub-unit include negative lenscomponents, and the second sub-unit includes a negative lens componentof a meniscus shape having a concave surface directed toward thereduction side.
 30. The single-focus optical system according to claim26, wherein: the first lens unit includes in order from the enlargementside, a first sub-unit and a second sub-unit, and all lens components inthe second sub-unit include negative lens components, and focusing iscarried out by moving the second sub-unit on an optical axis.
 31. Thesingle-focus optical system according to claim 26, wherein: the firstlens unit includes in order from the enlargement side, a first sub-unitand a second sub-unit, and the first sub-unit includes a reduction-sidepositive lens component closest to the reduction side, and all lenscomponents in the second sub-unit include negative lens components. 32.The single-focus optical system according to claim 26, wherein: thefirst lens unit includes in order from the enlargement side, a firstsub-unit and a second sub-unit, and all lens components in the secondsub-unit include negative lens components, and at the time of focusing,a distance between the first sub-unit and the second sub-unit, and adistance between the second sub-unit and the second lens unit change.33. The single-focus optical system according to claim 32, wherein thefirst sub-unit and the second lens unit are fixed at the time offocusing.
 34. The single-focus optical system according to claim 26,wherein: the first lens unit includes in order from the enlargementside, a first sub-unit and a second sub-unit, and the enlargement-sidenegative lens component is a single lens, and all lens components in thesecond sub-unit include negative lens components.
 35. The single-focusoptical system according to claim 26, wherein: the first lens unitincludes in order from the enlargement side, a first sub-unit and asecond sub-unit, and the first sub-unit includes the cemented lens, andall lens components in the second sub-unit include negative lenscomponents.
 36. The single-focus optical system according to claim 26,wherein: the first lens unit includes in order from the enlargementside, a first sub-unit and a second sub-unit, and the first sub-unitincludes the cemented lens and a reduction-side lens component, and thereduction-side lens component is disposed adjacent to the cemented lensin the first sub-unit, on the enlargement side of the cemented lens inthe first sub-unit, and a shape of the reduction-side lens component isa meniscus shape having a convex surface directed toward the enlargementside, and all lens components in the second sub-unit include negativelens components.
 37. The single-focus optical system according to claim26, wherein: the first lens includes in order from the enlargement side,a first sub-unit and a second sub-unit, and the second sub-unit includesonly the reduction-side negative lens component.
 38. The single-focusoptical system according to claim 26, wherein: the first lens unitincludes in order from the enlargement side, a first sub-unit and asecond sub-unit, and the first sub-unit includes in order from theenlargement side, the cemented lens and a plurality of positive lenscomponents, and the plurality of positive lens components is allpositive lens components that are adjacent, and all lens components inthe second sub-unit include negative lens components.
 39. Thesingle-focus optical system according to claim 34, wherein the followingconditional expression (1) is satisfied:0.75<SF₁₁<3.5   (1) where, SF₁₁=(R_(F11)+R_(R11))/(R_(F11)−R_(R11)), andhere R_(F11) denotes a radius of curvature of an enlargement-sidesurface of the enlargement-side lens component, and R_(R11) denotes aradius of curvature of a reduction-side surface of the enlargement-sidelens component.
 40. The single-focus optical system according to claim35, further comprising: a reduction-side lens component on theenlargement side of the cemented lens in the first sub-unit, wherein: ashape of the reduction-side lens component is a meniscus shape having aconvex surface directed toward the enlargement side, and the followingconditional expression (2) is satisfied:1.4<SF₁₂<15   (2) where, SF₁₂=(R_(F12)+R_(R12))/(R_(F12)−R_(R12)), andhere R_(F12) denotes a radius of curvature of an enlargement-sidesurface of the reduction-side lens component, and R_(R12) denotes aradius of curvature of a reduction-side surface of the reduction-sidelens component.
 41. The single-focus optical system according to claim35, wherein the following conditional expression (3) is satisfied:−15<SF ₁₃<−2.0   (3) where, SF₁₃=(R_(F13)+R_(R13))/(R_(F13)−R_(R13)),and here R_(F13) denotes a radius of curvature of an enlargement-sidesurface of the cemented lens in the first sub-unit, and R_(R13) denotesa radius of curvature of a reduction-side surface of the cemented lensin the first sub-unit.
 42. The single-focus optical system according toclaim 38, wherein: the plurality of positive lens components includes afront-side positive lens component which is positioned closest to theenlargement side, and a rear-side positive lens component which ispositioned closest to the reduction side, and the following conditionalexpression (4) is satisfied:0.10<SF ₁₄ −SF ₁₅<7.0   (4) where,SF₁₄=(R_(F14)+R_(R14))/(R_(F14)−R_(R14)), andSF₁₅=(R_(F15)+R_(R15))/(R_(F15)−R_(R15)), and here R_(F14) denotes aradius of curvature of an enlargement-side surface of the front-sidepositive lens component, R_(R14) denotes a radius of curvature of areduction-side surface of the front-side positive lens component,R_(F15) denotes a radius of curvature of an enlargement-side surface ofthe rear-side positive lens component, and R_(R15) denotes a radius ofcurvature of a reduction-side surface of the rear-side positive lenscomponent.
 43. The single-focus optical system according to claim 30,wherein: the second sub-unit includes only the reduction-side negativelens component, and the following conditional expression (5) issatisfied:0.80<SF₁₆<4.0   (5) where, SF₁₆=(R_(F16)+R_(R16))/(R_(F16)−R_(R16)), andhere R_(F16) denotes a radius of curvature of an enlargement-sidesurface of the reduction-side negative lens component in the secondsub-unit, and R_(R16) denotes a radius of curvature of a reduction-sidesurface of the reduction-side negative lens component in the secondsub-unit.
 44. The single-focus optical system according to claim 26,wherein: the first lens unit includes in order from the enlargementside, a first sub-unit and a second sub-unit, and the first sub-unitincludes a reduction-side positive lens component closest to thereduction side, and the reduction-side positive lens component is asingle lens, and all lens components in the second sub-unit includenegative lens components, and in a rectangular coordinate system inwhich a horizontal axis is let to be Nd1PR and a vertical axis is let tobe vd_(1PR), when a straight line represented byNd_(1PR)=α×vd_(1PR)+β_(1PR), where, α=−0.01, Nd_(1PR) and vd_(1PR) forthe reduction-side positive lens component are included in both of anarea determined by a straight line when a lower limit value of a rangeof the following conditional expression (11) is β_(1PR)=2.25, and anarea determined by the following conditional expressions (12) and (13):2.25≦β_(1PR)   (11),1.40<Nd_(1PR)   (12), and35<vd_(1PR)   (13) where, Nd_(1PR) denotes a refractive index of thereduction-side positive lens component, and vd_(1PR) denotes Abbe numberfor the reduction-side positive lens component.
 45. The single-focusoptical system according to claim 32, wherein: the second sub-unitincludes the reduction-side negative lens component, and thereduction-side negative lens component in the second sub-unit is asingle lens, and in a rectangular coordinate system in which ahorizontal axis is let to be Nd_(1NR) and a vertical axis is let to bevd_(1NR), when a straight line represented byNd_(1NR)=α×vd_(1NR)+β_(1NR), where, α=−0.01, Nd_(1NR) and vd_(1NR) forthe reduction-side negative lens component in the second sub-unit areincluded in both of an area determined by a straight line when a lowerlimit value of a range of the following conditional expression (14) isβ_(1NR)=2.15, and an area determined by the following conditionalexpressions (15) and (16):2.15≦β_(1NR)   (14),1.45<Nd_(1NR)   (15), and25<vd_(1NR)   (16) where, Nd_(1NR) denotes a refractive index of thereduction-side negative lens component in the second sub-unit, andvd_(1NR) denotes Abbe number for the reduction-side negative lenscomponent in the second sub-unit.
 46. The single-focus optical systemaccording to claim 26, wherein the enlargement-side lens component inthe first lens unit satisfies the following conditional expression (A):0<f/e _(N1F)<2   (A) where, f denotes a focal length of the overallsingle-focus optical system at the time of focusing to an object atinfinity, and e_(N1F) denotes a maximum effective aperture of theenlargement-side lens component in the first lens unit.
 47. Thesingle-focus optical system according to claim 26, further comprising:an aperture stop, wherein the following conditional expression (B) issatisfied:0<(f/e _(AS))/Fno<2   (B) where, f denotes a focal length of the overallsingle-focus optical system at the time of focusing to an object atinfinity, e_(AS) denotes a maximum diameter of the aperture stop, andFno denotes an F-number for the overall single-focus optical system atthe time of focusing to an object at infinity.
 48. The single-focusoptical system according to claim 26, wherein the following conditionalexpression (C) is satisfied:0<T _(air) _(_) _(max) /Σd≦0.27   (C) where, T_(air) _(_) _(max) is alargest axial air space in the range from a surface positioned closestto the enlargement side to a surface positioned closest to the reductionside in the single-focus optical system, and Σd is an axial distancefrom the surface positioned closest to the enlargement side to thesurface positioned closest to the reduction side in the single-focusoptical system.
 49. An optical apparatus comprising: an optical system;and an image pickup element which is disposed on a reduction side,wherein: the image pickup element has an image pickup surface, andconverts an image formed on the image pickup surface by the opticalsystem to an electric signal, and the optical system is the single-focusoptical system according to claim
 26. 50. An optical apparatuscomprising: an optical system; and a display element which is disposedon a reduction side, wherein: the display element has a display surface,and an image displayed on the display surface is projected on theenlargement side by the optical system, and the optical system is thesingle-focus optical system according to claim 26.